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Re: Question related to unique key
Posted by: Rick James
Date: March 16, 2009 10:48PM

Think of a PRIMARY KEY as the preferred way to unambiguously identify each row in the table. Ok, maybe you could envision a row as being identified by 'null', but why bother.

Another note: KEY is the same as INDEX. Neither implies uniqueness.

A common PRIMARY KEY is
This assigns a number (1,2,...) to each row (assuming you don't explicitly set it).

An INSERT will spit at you if you violate a UNIQUEness constraint.

MyISAM does not require any keys.
InnoDB requires a PRIMARY KEY, even to the point of providing one if you don't specify one.

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Written By
March 16, 2009 07:43AM
Re: Question related to unique key
March 16, 2009 10:48PM

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